1. Field of the Invention
This invention relates to shock absorbing devices, and more particularly to an energy absorbing device utilizing compressibility of resistant materials in conjunction with hydraulic principles.
2. Description of the Prior Art
Energy absorbing devices based on the hydraulic principle generally comprise a cylinder having one closed end and an open end for introduction of a piston which is adapted to apply a force to a fluid within the cylinder. The cylinder, at its closed end, is secured to a first member and a free end of the piston is secured to another member which is relatively movable with respect to the first member. Orifice means are provided to permit movement of fluid from one side of the piston to the backside of the piston. The free end of the piston extends through a cap enclosing the other end of the cylinder. To avoid leakage of the fluid in the area of the cap encompassing the sliding piston rod, it is necessary to incorporate a seal. To prevent premature wearing out of the seal, it is necessary to expend time in polishing the surface of the piston rod. But even so, after a period of use, the seal will be worn and eventually leaking will occur. Therefore, it will be necessary either to apply further pressure on the seal to grip the piston rod in a more secure way, or it is necessary to totally replace the seal.
Another problem associated with hydraulic devices is the wear of a resilient seal mounted on the piston and engaging the inner surface of the cylinder. After a protracted period of use, the piston seal will be worn, and fluid leakage will occur, thereby changing the energy absorbing capability of the hydraulic device. To avoid the disadvantages described with respect to the hydraulic energy absorber devices, non-hydraulic energy absorbing devices have been developed based on the principle of using force absorption elastomer materials. For example, U.S. Pat. No. 4,756,512 overcomes the deficiencies associated with struts employing hydraulic principles by designing a suspension strut using elastomer material pads assembled in stacks, as sold by Miner Enterprises, Inc., of Geneva, Ill., under the trademark (TECSPAK), and more fully described in U.S. Pat. No. 4,198,037. Such strut assembly comprises a pair of telescoped tubes housing therein a stack of elastomer material pads, each having a central opening for admitting a steel guide rod. The pads are separated from each other by intervening steel plates. One disadvantage of an energy-absorbing device using only elastomer pads is the large number of pads that have to be assembled to absorb sufficient energy under a particular force application.